Method for producing a shaped part

ABSTRACT

To make a shaped article, a decorative paper whose cotton linters content is at least 10 wt % and can be as high as 100 wt % of the total fiber content in the paper is impregnated with a cross-linkable aminoplastic resin, applied on a carrier of wood-based material and formed to a three-dimensional structure under pressure and at elevated temperature while the resin undergoes cross-linking.

DESCRIPTION

The invention relates to a method for making a shaped article.

The object of the invention is to provide a method for making a shapedarticle with a thermoset plastic surface having three-dimensionalstructure, especially for furniture and components of wood andwood-based materials.

In the method that achieves this object, a decorative paper whose cottonlinters content is at least 10 wt % and can be as high as 100 wt % ofthe total fiber content in the paper is impregnated with across-linkable aminoplastic resin, applied on a carrier of wood-basedmaterial and formed to a three-dimensional structure under pressure andat elevated temperature while the resin undergoes cross-linking.

Forming is preferably achieved by pressing.

The cotton linters are obtained from lint of natural origin, which canbe processed in suitable manner.

Decorative paper is usually manufactured on the basis of cellulosicmaterial as the only fibrous material. According to the teaching of theinvention, the cellulosic material can be replaced entirely or partly bycotton linters, so that the fiber content of the paper is composed ofcotton linters or a mixture of cotton linters and cellulosic material.

Cellulosic material is almost pure cellulose. The mixture of cottonlinters and cellulosic material is therefore substantially a mixture ofcotton linters and cellulose.

Cotton linters can be processed alone or together with cellulosicmaterial on a papermaking machine in exactly the same way as purecellulosic material. It is self-evident that the decorative paper usedaccording to the invention can contain not only the fibrous material butalso the other usual constituents of a decorative paper, such as fillersand pigments.

Paper containing cotton linters as fiber constituent is known for otherapplications. In U.S. Pat. No. 5,089,327 A, for example, paper with acotton linters content of 8% to 16% is impregnated in a size press untilsaturated with a polymer acting as an antistatic agent. The web obtainedis further processed to a multi-layer high-pressure laminate. Thelaminate is a flat product. Three-dimensional forming is not applied.

U.S. Pat. No. 4,061,823 A relates to a high-pressure laminate whose corelayers comprise cotton linters in paper form and contain cured phenolresin. This laminate is also a flat product and not a three-dimensionalshaped article.

In a preferred alternative embodiment, carrier and decorative paper areformed together. This is preferably achieved by pressing in a stamping(in-mold) press.

In another preferred alternative embodiment, a carrier having athree-dimensional surface contour is used and the decorative paper isformed to match this contour. This is preferably achieved by pressing ina membrane press.

Preferably there is used a decorative paper whose fiber content iscomposed of cotton linters and cellulosic material. The content ofcotton linters should be 10 to 80 wt %, preferably 20 to 80 wt % of thetotal fiber content in the paper.

The decorative paper used according to the invention has a weight of 40to 200 g/m². It is a voluminous paper of high absorbency, flexibilityand tearing strength. The large volume and high absorbency of the paperensure maximum resin uptake during the impregnation process.

The paper can be printed. Gravure or screen printing is possible forarticles made in large series, preferably with the water-basedprinting-ink system that is customary for decorative printing. Digitalprinting is conceivable for small series and special products.

In a preferred alternative embodiment there is used a decorative paperwith a surface application of a buffer system that controls the curingreaction of aminoplastic resin. The buffer system is applied onto thedecorative paper with a suitable applicator machine, such as a sizepress.

In another preferred alternative embodiment, there is used a decorativepaper with incorporation into the pulp of a buffer system that controlsthe curing reaction of aminoplastic resin. The buffer system isincorporated into the pulp, which is eventually processed on thepapermaking machine.

In a preferred alternative embodiment, a wood-fiber mat, wood-basedchipboard or wood-based fiberboard, especially hard fiberboard,medium-density fiberboard or high-density fiberboard is used as thecarrier.

In a preferred alternative embodiment, the decorative paper is appliedin one layer on the carrier.

The invention will be explained in more detail hereinafter on the basisof examples.

EXAMPLE 1

Decorative paper with a high fiber content of cotton linters isimpregnated with an aminoplastic resin. Thereafter the paper is driedand applied on a carrier of wood-based material, such as a wood-fibermat, hard fiberboard, medium-density fiberboard or high-densityfiberboard.

Carrier and paper are formed to a three-dimensional structure in astamping (in-mold) press. Three-dimensional forming is to be understoodas forming in length, width and height.

The stamping press has embossing dies in the form of a male die and afemale die, between which carrier and paper are pressed together. Themale and female dies have a complementary surface contour, whichrepresents a perfect negative of the pressed article. In this type ofpress the carrier is coformed.

The carrier and the decorative paper impregnated with aminoplastic resinare exposed together to a pressure of more than 100 bar (10 MPa) and atemperature of 100° C. to 140° C. and pressed for a duration of 1 to 5minutes in 1 step. At the same time the aminoplastic resin undergoescross-linking and the entire structure is molded.

The resin can contain suitable catalysts (hardeners) for the process ofcross-linking and curing.

After the pressing process, a blank with a thermoset (heat-cured)plastic surface layer is obtained. The blank can be further processed inthe furniture industry to a thermoset plastic furniture surface.

Compared with conventional thermoplastic furniture surfaces, theinventive thermoset plastic furniture surface is characterized by betterscratch resistance, heat resistance, bonding to the carrier material,fastness to light, resistance to chemicals and suitability forrecycling.

EXAMPLE 2

A carrier with a predetermined three-dimensional surface contour isused. An appropriately premilled medium-density fiberboard is cited asan example.

The decorative paper impregnated with aminoplastic resin is applied onthe carrier and introduced together therewith into the pressure-tightpressing chamber of a membrane press. The pressing chamber is outgassedby application of a vacuum. Using a membrane preheated to 100° C. to120° C., the carrier and decorative paper are then pressed together inone working cycle at a pressure of 5 to 18 bar (0.5 to 1.8 MPa). Thepressure is applied by compressed air or heated oil. The duration of thepressing process is about 1 to 5 minutes.

In the membrane press, only the impregnated decorative paper is formed.It conforms to the predetermined surface contour of the carrier andforms thereon a thermoset (heat-cured) plastic surface layer. In thistype of press the carrier is not conformed.

RESULT

The decorative paper used withstands the loads imposed during stampingpressing and membrane pressing with simultaneous forming of the paperand curing of the aminoplastic resin. No cracking occurs. The criticalfactor in this process is that cotton linters account for at least 10 wt% of the fiber content of the paper. As a result, a thermoset plasticsurface layer formed with three-dimensional structure is obtained forthe first time by pressing a decorative paper.

1. A method for making a shaped article comprising the steps of: a)impregnating a decorative paper whose cotton linters content is in therange of at least 10% by weight of the total fiber content in the paperwith a cross-linkable aminoplastic resin; b) applying said decorativepaper to a carrier of wood-based material which has a three-dimensionalsurface contour; and c) subjecting said carrier and decorative paper topressure and an elevated temperature while the resin undergoescross-linking and forming the decorative paper to match the contour ofthe carrier, thus making in one step a three-dimensional structure,wherein said cross-linking of said resin occurs only in step c).
 2. Amethod according to claim 1, wherein said forming step of subjectingsaid carrier and decorative paper to pressure is achieved by pressing.3. A method according to claim 2, wherein said pressing is performed ina stamping press.
 4. A method according to claim 1, wherein saiddecorative paper is a decorative paper whose fiber content is composedof cotton linters and cellulosic material.
 5. A method according toclaim 1, wherein said decorative paper is a decorative paper whosecontent of cotton linters is in the range of 10 to 80% by weight of thetotal fiber content in the paper.
 6. A method according to claim 1,wherein said decorative paper is a printable decorative paper.
 7. Amethod according to claim 1, wherein said decorative paper is adecorative paper with a surface application of a buffer system thatcontrols the curing reaction of aminoplastic resin.
 8. A methodaccording to claim 1, wherein said decorative paper is a decorativepaper having pulp incorporated with a buffer system that controls thecuring reaction of aminoplastic resin.
 9. A method according to claim 1,wherein said carrier comprises a member selected from the groupconsisting of a wood-fiber mat, wood-based chipboard and wood-basedfiberboard.
 10. A method according to claim 1, wherein said decorativepaper is applied in one layer on said carrier.
 11. A method according toclaim 2, wherein said pressing is performed in a membrane press.
 12. Amethod according to claim 5, wherein said content of cotton linters is20 to 80% by weight of the total fiber content in the paper.
 13. Amethod according to claim 9, wherein said carrier is selected from thegroup consisting of hard fiberboard, medium density fiberboard, and highdensity fiber board.
 14. A method according to claim 1, wherein saiddecorative paper is a decorative paper whose fiber content is solelycotton linters.